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Roubi posted a nice video about making an 1/4 wave SMA antenna. The real world lengths (wavelength/frequency) are not always mathematically correct since the transmitter or receiver case is not an infinite ground plane. Below is the data sheet with a PDF that comes with one of our antenna kits with the lengths that we found ideal on a network analyzer for our metal transmitters. Just make sure the 6" reference line measures 6" (15.24 cm) when you print it out. If not, tweak your print zoom plus or minus to get a 6" length on the page. You can find other antenna kits on the site for BNC's ,etc.

Roubi posted a nice video about making an 1/4 wave SMA antenna. The real world lengths (wavelength/frequency) are not always mathematically correct since the transmitter or receiver case is not an infinite ground plane. Below is the data sheet with a PDF that comes with one of our antenna kits with the lengths that we found ideal on a network analyzer for our metal transmitters. Just make sure the 6" reference line measures 6" (15.24 cm) when you print it out. If not, tweak your print zoom plus or minus to get a 6" length on the page. You can find other antenna kits on the site for BNC's ,etc.

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But here is a question : how the diameter of the antenna affects the signal ? Here, I am using a 0.6mm cable but would a 1mm or 1.5mm add anything ?

Thanks

Hi Roubi,

The fatter the wire, the wider the bandwidth of the quarter wave vertical up to about a 5% thickness of the length. For a 6" antenna that would be 0.3" thick wire (!) which is not practical at all. As a rule, use as fat a wire as is practical considering it has to bend without breaking the SMA pin or hurting the talent. So pick something that is tough and flexible and go from there. I would pick comfort over small bandwidth improvements but also, there is no reason to use hair thin wire.

As a fat example, note the width of the arms on the Lectro SNA dipole antenna; those widths were chosen for the best bandwidth improvement possible. Anything wider than that had negligible improvement. That width is totally impractical for a transmitter whip.

Best Regards,

Larry Fisher

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The fatter the wire, the wider the bandwidth of the quarter wave vertical up to about a 5% thickness of the length. For a 6" antenna that would be 0.3" thick wire (!) which is not practical at all. As a rule, use as fat a wire as is practical considering it has to bend without breaking the SMA pin or hurting the talent. So pick something that is tough and flexible and go from there. I would pick comfort over small bandwidth improvements but also, there is no reason to use hair thin wire.

As a fat example, note the width of the arms on the Lectro SNA dipole antenna; those widths were chosen for the best bandwidth improvement possible. Anything wider than that had negligible improvement. That width is totally impractical for a transmitter whip.

Best Regards,

Larry Fisher

Thanks for the quick answer.

Practically speaking,would going from a 0.6mm diameter to 1mm change a lot ? I kind of feel lazy thinking about redoing all my antennas...

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Here are some of the antennas I make. One of the tests I do is to put the SMA connector into a vice and then I lock vice grip pliers

on the antenna wire. I then try to rip the antenna wire out off the SMA. Lectrosonics antennas are super strong. I pulled a Remote Audio antenna wire out, but it was difficult. Mine are 3rd place so far.

You might think it is crazy to put a $40.00 antenna in a vice and then try to destroy it, but I wanted to know. I also did not want "talent" pulling an antenna out.

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Go with what you've used. Next to a body, most of this stuff is out the window anyway.

Best Regards,

Larry Fisher

Merci beaucoup Larry, I'll sleep better not feeling the urgent need to remake all of them...

1 hour ago, mark kirchner said:

Roubi,

Here are some of the antennas I make. One of the tests I do is to put the SMA connector into a vice and then I lock vice grip pliers

on the antenna wire. I then try to rip the antenna wire out off the SMA. Lectrosonics antennas are super strong. I pulled a Remote Audio antenna wire out, but it was difficult. Mine are 3rd place so far.

You might think it is crazy to put a $40.00 antenna in a vice and then try to destroy it, but I wanted to know. I also did not want "talent" pulling an antenna out.

Impressive Mark,

I haven't been as far as you!

I am using the antennas only on receivers (I am using UWP-D11 modified to SMA) but also quickly tried them with Lectro SRB (even at the wrong length, they work very well).

What wire are you using ?

And where do you find those small caps ?

Thanks

Roubi (Grégoire de Courtivron)

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I have made antennas from nitinol nickel-titanium wire, but decided to use small diameter multi-strand cable instead. I understand that you are making antennas for receivers, not transmitters at this point. When I made nickel-titanium antennas, I would file a series of small notches in the terminal end of the wire. The notches would be covered by the SMA pin after soldering, but would add a mechanical bound inside the soldered connection.

The colored caps are sold at B&H in New York, made by Lectrosonics I think.

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I have made antennas from nitinol nickel-titanium wire, but decided to use small diameter multi-strand cable instead. I understand that you are making antennas for receivers, not transmitters at this point. When I made nickel-titanium antennas, I would file a series of small notches in the terminal end of the wire. The notches would be covered by the SMA pin after soldering, but would add a mechanical bound inside the soldered connection.

The colored caps are sold at B&H in New York, made by Lectrosonics I think.

Hi Mark,

The tension on the antenna when I close the rain protection of the bag is my only concern about this antenna. It doesn't seem to be a huge tension, but still it is there… So I understand the choice of multi strand cable : more flexible. On the other hand, I love the fact that my antenna are straight and always are.

When cutting the antennas, my pliers doesn't do a clean cut and the little"imperfection" it leaves is perfect to hold the antenna in the solder "bubble". I thought about using a dremel though.

Thanks for the link at B&H. I'll need to find something else though, as I am in west Africa.

The 50 Ohms is just the impedance of the whip antenna resonating in free space. The fact that it has to be resonate to match to the 50 Ohms of your antenna input or output is why the resonate length is somewhat critical. Space itself is 377 Ohms as I (and Google) remember. The antenna resonates in order to match that 377 Ohms to 50 Ohms. The material of the wire has almost nothing to do with it since the any 6" wire's resistance is probably less than a tenth of an Ohm.

In sum, the wire could be silver or lead with the same performance. Price wise, some people think our antennas are made from gold.

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Also Chris, tin (presolder) that steel wire before you try soldering it to the center pin. The steel wire will take much longer to solder and you don't want to destroy the insulation around the pin. Another also: clean all the oil off that wire if there is any and you might use a mild soldering flux on just the wire before you tin it.

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Also Chris, tin (presolder) that steel wire before you try soldering it to the center pin. The steel wire will take much longer to solder and you don't want to destroy the insulation around the pin. Another also: clean all the oil off that wire if there is any and you might use a mild soldering flux on just the wire before you tin it.

Best Regards,

Larry Fisher

Hey Larry,

This isn't quite SMA related, but it seems like a fitting topic. I have a bunch of block 25 fixed antenna gear that need replacement antennas - LMa's, UCR100's, etc. Can I apply the same Lectrosonics SMA antenna cutting guides to their antenna lengths? i.e. an SMA block 25 antenna is the same length as a fixed antenna measured outside the body of the receiver or transmitter?

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This isn't quite SMA related, but it seems like a fitting topic. I have a bunch of block 25 fixed antenna gear that need replacement antennas - LMa's, UCR100's, etc. Can I apply the same Lectrosonics SMA antenna cutting guides to their antenna lengths? i.e. an SMA block 25 antenna is the same length as a fixed antenna measured outside the body of the receiver or transmitter?

You would be pretty close, particularly on the mid blocks. All whip antennas are matched to the case (a very oddly shaped ground plane) of the particular device. It probably doesn't make a lot of difference, but if when Lectro is making thousands of them, we might as well measure the antenna and device together and get the right length. I recommend you send an email to service@lectrosonics.com and ask for the correct length for your particular block 25 devices. They should give you an answer pretty quickly. Let me know if you don't get an answer in a few days, though I can't imagine it.

Best Regards,

Larry Fisher

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You would be pretty close, particularly on the mid blocks. All whip antennas are matched to the case (a very oddly shaped ground plane) of the particular device. It probably doesn't make a lot of difference, but if when Lectro is making thousands of them, we might as well measure the antenna and device together and get the right length. I recommend you send an email to service@lectrosonics.com and ask for the correct length for your particular block 25 devices. They should give you an answer pretty quickly. Let me know if you don't get an answer in a few days, though I can't imagine it.

Best Regards,

Larry Fisher

Thanks Larry!

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The best Leatherman for me : strong, only what I need, and nothing to loose (like those with several screwdriver heads you can add to the body). And yes the pliers function is awesome : https://www.leatherman.com/crunch-1.html